Laminated linear motor stator core

ABSTRACT

A linear motor ( 15 ) comprising a stator ( 16 ) having an opening ( 18 ), a mover ( 19 ) disposed in the opening and configured and arranged to reciprocate linearly in an axial direction (x-x) relative to the stator, the stator comprising a first pole section ( 21 ) and a second pole section ( 22 ) stacked in the axial direction and forming a recess ( 26 ) between them for receiving annular windings, the first pole section comprising a first laminate ( 17   a ) having a first cross-sectional geometry ( 29 ) and a second laminate ( 17   b ) having a second cross-sectional geometry ( 30 ) different from the first cross-sectional geometry, and the first laminate and the second laminate stacked in the axial direction.

TECHNICAL FIELD

The present invention relates generally to linear motors, and moreparticularly to a laminated stator and method of assembly for a linearmotor.

BACKGROUND ART

Linear motors are known in the prior art. Conventional linear motorsgenerally comprise a mover that reciprocates through the field of astator due to magnetic forces generated by energized coils in thestator. Normally the stator is stationary and drives the mover in anaxial direction. However, it is possible to make the mover stationaryand have the stator drive itself in an axial direction. Accordingly, theaxial direction is the linear direction of movement for either the moveror stator, depending on which of them is to move in relation to theother. The stator conventionally includes at least one coil wound in atleast one stator core. The stator coil may be a single winding connectedto an electrical supply unit or a distributive winding. The purpose ofthe stator coils is to generate magnetic flux that interacts withpermanent magnets on the mover. Thus, a conventional linear motorincludes a generally cylindrical outer stator core, stator coils woundwithin the stator core, and an inner mover having permanent magnets andthat moves linearly in an axial direction relative to the stator core soas to provide linear motion by means of interaction with the magneticfield of the stator.

Various stator assembly configurations are known. For example, U.S. Pat.No. 6,603,224, entitled “Linear Motor Stator Assembly Piece,” disclosesa stator for a linear motor that is built by stacking module parts. U.S.Pat. No. 6,289,575, entitled “Method of Manufacturing a Stacked StatorAssembly for a Linear Motor,” discloses a method of manufacturing astator from individual pieces assembled around a removable form. U.S.Pat. No. 7,378,763, entitled “Linear Motor,” discloses a stator coredivided into two parts with each of the parts being made of a softmagnetic powder. U.S. Pat. No. 7,884,508, entitled “Linear Motor”, alsodiscloses a stator core divided into two parts formed of a soft magneticpowder and a mover that has at least one section also formed of a softmagnetic material. U.S. Pat. No. 6,060,810, entitled “Stator for LinearMotor by Staggered Core Lamination,” discloses a stator for a linearmotor formed from radially-extending laminates. Each of these U.S.patents is incorporated herein by reference.

BRIEF SUMMARY OF THE INVENTION

With parenthetical reference to corresponding parts, portions orsurfaces of the disclosed embodiment, merely for the purposes ofillustration and not by way of limitation, the present inventionprovides a linear motor (15) comprising a stator (16) having an opening(18), a mover (19) disposed in the opening and configured and arrangedto reciprocate linearly in an axial direction (x-x) relative to thestator, the stator comprising a first pole section (21) and a secondpole section (22) stacked in the axial direction and forming a recess(26) between them for receiving annular windings, the first pole sectioncomprising a first laminate (17 a) having a first, cross-sectionalgeometry (29) and a second laminate (17 b) having a secondcross-sectional geometry (30) different from the first cross-sectionalgeometry, and the first laminate and the second laminate stacked in theaxial direction.

The first pole section may further comprise a third laminate (17 c)having a third cross-sectional geometry (33) different from the firstcross-sectional geometry and the second cross-sectional geometry andstacked in the axial direction with the first laminate and the secondlaminate. The first pole section may further comprise a fourth laminate(17 d) having the first cross-sectional geometry (29) and stacked in theaxial direction with the first, second and third laminates.

The first pole section may comprise multiple laminates having the firstcross-sectional geometry and multiple laminates having the secondcross-sectional geometry and stacked in the axial direction. The firstcross-sectional geometry (29) of the first laminate may comprise anannular ring (35) having an outer perimeter (36) and an inner perimeter(37). The annular ring may comprise an opening (38) between the outerperimeter and the inner perimeter. The second cross-sectional geometry(30, 33) of the second laminate may comprise an annular ring (39, 55)having an outer perimeter (40, 56) and an inner perimeter (41, 57) and aradial thickness (42, 58) between them greater than a radial thickness(60) of the annular ring of the first cross-sectional geometry. Theannular ring (55) of the second cross-sectional geometry (33) of thesecond laminate may comprise a shaped opening (59) between the outerperimeter (56) and the inner perimeter (57). The annular ring (39) ofthe second cross-sectional geometry (30) of the second laminate maycomprise a first face (39 a) and a second face and an opening (44)between the first face and the second face. The annular ring of thesecond cross-sectional geometry (30) of the second laminate may furthercomprise a notch (43) extending towards the inner perimeter (41) fromthe outer perimeter (40).

The linear motor may further comprise a center ring (70 b) within thefirst pole section (21) and defining the opening of the stator. Thecenter ring element may comprise an inner perimeter (76) configured todefine at least in part the stator opening and an outer perimeter (74)configured to fit at least in part within the inner perimeter (41, 57)of the first pole section (21), a first facing surface (71) and a secondfacing surface (75), and the first facing surface skewed relative to animaginary plane (y-y) oriented generally perpendicular to the axialdirection (x-x) of the mover such that the first facing surface is notparallel to the plane oriented generally perpendicular to the axialdirection of the mover. The second facing surface (75) may be skewedrelative to the plane (y-y) perpendicular to the axial direction and maybe parallel to the first facing surface (71). The first pole section(21) may comprise a first facing surface (39 b) orientated in a plane(y-y) generally perpendicular to the axial direction (x-x) of the moverand the outer perimeter of the center ring element may comprise an axialalignment projection (79 b) configured and arranged to extend radiallyoutward at least in part beyond the inner perimeter (41, 57) of thefirst pole section (21) and to abut against the first facing surface (39b) of the first pole section (21). The axial alignment projection maycomprise an annular contact surface (73) oriented in a plane (y-y)generally perpendicular to the axial direction of the mover. The centerring element may comprise a solid unitary steel tube.

The second pole section (22) may comprise a first laminate (17 e) havinga first cross-sectional geometry (29) and a second laminate (17 f)having a second cross-sectional geometry (31) different from the firstcross-sectional geometry, and the first laminate and the second laminatestacked in the axial direction. The second pole section may furthercomprise a third laminate (17 g) having a third cross-sectional geometry(32) different from the first cross-sectional geometry and the secondcross-sectional geometry and stacked in the axial direction with thefirst laminate and the second laminate. The second pole section mayfurther comprise a fourth laminate (17 h) having the firstcross-sectional geometry (29) and stacked in the axial direction withthe first, second and third laminates.

The second pole section may comprise multiple laminates having the firstcross-sectional geometry and multiple laminates having the secondcross-sectional geometry and stacked in the axial direction. The firstcross-sectional geometry (29) of the first laminate may comprise anannular ring (35) having an outer perimeter (36) and an inner perimeter(37). The annular ring may comprise an opening (38) between the outerperimeter and the inner perimeter. The second cross-sectional geometry(31, 32) of the second laminate may comprise an annular ring (45, 50)having an outer perimeter (46, 51) and an inner perimeter (47, 52) and aradial thickness (48, 53) between them greater than a radial thickness(60) of the annular ring of the first cross-sectional geometry. Theannular ring (50) of the second cross-sectional (32) of the secondlaminate may comprise a shaped opening (54) between the outer perimeter(51) and the inner perimeter (52). The annular ring of the secondcross-sectional geometry (31) of the second laminate may comprise anotch (49) extending towards the inner perimeter (447) from the outerperimeter (46).

The linear motor may further comprise a center ring (70 c) within thesecond pole section (22) and defining the opening of the stator. Thecenter ring element may comprise an inner perimeter (76) configured todefine at least in part the stator opening and an outer perimeter (74)configured to fit at least in part within the inner perimeter (47, 52)of the second pole section (21), a first facing surface (71) and asecond facing surface (75), and the first facing surface skewed relativeto an imaginary plane (y-y) oriented generally perpendicular to theaxial direction (x-x) of the mover such that the first facing surface isnot parallel to the plane oriented generally perpendicular to the axialdirection of the mover. The second facing surface (75) may be skewedrelative to the plane (y-y) perpendicular to the axial direction and maybe parallel to the first facing surface (71). The second pole section(22) may comprise a first facing surface (45 b) orientated in a plane(y-y) generally perpendicular to the axial direction (x-x) of the moverand the outer perimeter of the center ring element may comprise an axialalignment projection (79 c) configured and arranged to extend radiallyoutward at least in part beyond the inner perimeter (47, 52) of thefirst pole section and to abut against the first facing surface (45 b)of the second pole section (22). The axial alignment projection maycomprise an annular contact surface (73) oriented in a plane (y-y)generally perpendicular to the axial direction of the mover.

The first pole section (21) may comprise a first center ring element (70b) and the second pole section (22) may comprise a second center ringelement (70 c), wherein each of the first center ring element and thesecond center ring element comprise an inner perimeter (76) configuredto define at least in part the stator opening and an outer perimeter(74) configured to fit at least in part within the inner perimeter ofthe respective pole section (41, 57 and 47, 52), a first facing surface(71) and a second facing surface (75), and the first and second facingsurface skewed relative to an imaginary plane (y-y) orientated generallyperpendicular to the axial direction (x-x) of the mover such that thefirst and second facing surface are not parallel to the plane orientedgenerally perpendicular to the axial direction of the mover, wherein theskew of the second facing surface of the first center ring element ofthe first pole section is substantially equal to the skew of the firstfacing surface of the second center ring element of the second polesection, and wherein the first center ring element and the second centerring element are stacked in the axial direction to form at least in partthe opening of the stator. The skew may be configured and arranged toreduce cogging forces in the motor.

In another aspect, a linear motor is provided comprising a stator (16)having an opening (18), a mover (19) disposed in the opening andconfigured and arranged to reciprocate the linearly in an axialdirection (x-x) relative to the stator, the stator comprising a firstpole section (21) and a second pole section (22) stacked in the axialdirection and forming a recess (26) between them for receiving annularwindings, the first pole section having an outer perimeter (36, 40, 56)and an inner perimeter (41, 57), a center ring element (70 b) having aninner perimeter (76) configured to define at least in part the statoropening and an outer perimeter (74) configured to fit at least in partwithin the inner perimeter of the first pole section, the center ringelement further comprising a first facing surface (71) and a secondfacing surface (75), and the first facing surface skewed relative to animaginary plane (y-y) orientated generally perpendicular to the axialdirection (x-x) of the mover such that the first facing surface is notparallel to the plane orientated generally perpendicular to the axialdirection of the mover.

The second facing surface may be skewed relative to the plane (y-y)perpendicular to the axial direction (x-x) and may be parallel to thefirst facing surface. The first pole section (21) may comprise a firstfacing surface (39 b) orientated in a plane (y-y) generallyperpendicular to the axial direction of the mover and the outerperimeter of the center ring element may comprise an axial alignmentprojection (79 b) configured and arranged to extend radially outward atleast in part beyond the inner perimeter (41, 57) of the first polesection and to butt against the first facing surface (39 b) of the firstpole section (21). The axial alignment projection may comprise anannular contact surface (73) orientated in a plane (y-y) generallyperpendicular to the axial direction of the mover. The center ringelement may comprise a solid unitary steel tube.

The first pole section and the second pole section may be provided witha rotational alignment contour (87) and the rotational alignment contourmay comprise an axial notch.

The first stator pole section (21) may comprise a pole sectionrotational alignment contour (87) corresponding to a first rotationalalignment key (82) of a ring rotational alignment fixture (81) and thecenter ring element (70) may comprise a ring rotational alignmentcontour (80) corresponding to a second rotational alignment key (83) ofthe ring rotational alignment fixture. The pole section rotationalalignment contour may comprise an axial notch (38), the first rotationalalignment key may comprise a tab (82) corresponding to the notch, thering rotational alignment contour may comprise an axial notch (80), andthe second rotational alignment key may comprise a protrusion (83)corresponding to the notch of the ring rotational alignment contour.

In another aspect, a method of forming a stator core of a linear motoris provided comprising the steps of forming a plurality of firstlaminates (17 a) having a first cross-sectional geometry (29), forming aplurality of second laminates (17 b, 17 c, 17 f, 17 g) having a secondcross-sectional geometry (30, 31, 32, 33) different from the firstcross-sectional geometry, stacking the plurality of first laminates andthe plurality of second laminates in an axial direction (x-x) to form atleast in part a first stator pole (21) section having an inner perimeter(41, 57), stacking the plurality of the first laminates and theplurality of the second laminates in an axial direction to form at leastin part a second stator pole section (22) having an inner perimeter (47,52), forming a first skewed center ring element (17 b), forming a secondskewed center ring element (17 c), pressing at least a portion (74) ofthe first skewed center ring element into the inner perimeter of thefirst stator pole section, pressing at least a portion of the secondskewed center ring element (74) into the inner perimeter of the secondstator pole section, and stacking the first pole section and the secondpole section in the axial direction so as to form a recess (26) betweenthem for receiving annular windings, and so that the first skewed centerring element and the second skewed center ring element form at least inpart an opening (18) for receiving a mover (19) configured and arrangedto reciprocate linearly in the axial direction (x-x) relative to thefirst and second stacked stator pole sections.

Each of the first skewed center ring element and the second skewedcenter ring element may comprise an inner perimeter (76) configured todefine at least in part the stator opening and an outer perimeter (74)configured to fit at least in part within the inner perimeter of therespective pole section, a first facing surface (71) and a second facingsurface (75), and the first and second facing surfaces skewed relativeto an imaginary plane (y-y) orientated generally perpendicular to theaxial direction of the mover such that the first and second facingsurfaces are not parallel to the plane orientated generallyperpendicular to the axial direction of the mover, and the steps ofpressing at least a portion of the first skewed center ring element intothe inner perimeter of the first stator pole section and pressing atleast a portion of the second skewed center ring element into the innerperimeter of the second stator pole section may comprise rotationallyaligning the first skewed center ring element and the second skewedcenter ring element such that the first facing surface and the secondfacing surface of the first skewed center ring element and the firstfacing surface and the second facing surface of the second skewed centerring element are all substantially parallel.

The plurality of first laminates and the plurality of second laminatesmay be provided with a rotational alignment contour (38, 43, 49, 54, 59)and the step of stacking the plurality of the first laminates and theplurality of the second laminates in an axial direction may comprise thesteps of providing a stator laminate assembly fixture (100, 103),rotationally aligning the stator laminate assembly fixture with therotational alignment contours of the laminates, and stacking thelaminates with the stator laminate assembly fixture such that the statorlaminate assembly fixture corresponds with the alignment contour of eachof the laminates so as to provide a desired rotational alignment of thelaminates relative to each other. The rotational alignment contour maycomprise an axial notch (38, 43, 49, 54, 59) having a first edge (85 a)and a second edge (85 b) spaced apart from the first edge, and thestator laminate assembly fixture may comprise a first axial rod (86 a)and a second axial rod (86 b) spaced apart from the first rod.

The first stator pole section may be provided with a pole sectionalignment contour (87), the first skewed center ring element and thesecond skewed center ring element may be each provided with a ringalignment contour (80), and the step of pressing at least a portion ofthe first skewed center ring element into the inner perimeter of thefirst stator pole section may comprise the steps of providing a ringalignment fixture (81) having a first rotational alignment key (82)corresponding to the pole section alignment contour and a secondrotational alignment key (83) corresponding to the ring alignmentcontour, rotationally aligning the first rotational alignment key withthe pole section alignment contour and the second rotational alignmentkey with the ring alignment contour, and pressing at least a portion ofthe first skewed center ring element into the inner perimeter of thefirst stator pole section such that the first rotational alignment keycorresponds with the pole section alignment contour and the secondrotational alignment key corresponds with the ring alignment contour, soas to provide a desired rotational alignment of the first pole sectionand the first skewed center ring element relative to each other.

The first pole section alignment contour may comprise an axial notch(38), the first rotational alignment key may comprise a tab (82)corresponding to the notch, the ring alignment contour may comprise anaxial notch (80), and the second rotational alignment key may comprise aprotrusion (83) corresponding to the notch of the ring alignmentcontour.

The second stator pole section (22) may be provided with a pole sectionalignment contour (87) and the step of pressing at least a portion ofthe second skewed center ring element into the inner perimeter of thesecond stator pole section may comprise the steps of providing an ringalignment fixture having a first rotational alignment key (82)corresponding to the pole section alignment contour and a secondrotational alignment key (83) corresponding to the ring alignmentcontour, rotationally aligning the first rotational alignment key withthe pole section alignment contour and the second rotational alignmentkey with the ring alignment contour, and pressing at least a portion ofthe second skewed center ring element into the inner perimeter of thesecond stator pole section such that the first rotational alignment keycorresponds with the pole section alignment contour and the secondrotational alignment key corresponds with the ring alignment contour soas to provide a desired rotational alignment of the second pole sectionand the second skewed center ring element relative to each other. Thesecond pole section alignment contour may comprise an axial notch (38),the first rotational alignment key may comprise a tab (82) correspondingto the notch, the ring alignment contour may comprise an axial notch(80), and the second rotational alignment key may comprise a protrusion(83) corresponding to the notch of the ring alignment contour.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal vertical cross-sectional view of the firstembodiment of the linear motor assembly.

FIG. 2 is a right perspective view of a first pole section shown in FIG.1.

FIG. 3 is an exploded view of the pole section shown in FIG. 2.

FIG. 4 is a right plan view of the pole section shown in FIG. 2.

FIG. 5 is a vertical cross-sectional view of the pole section shown inFIG. 4, taken generally on line B-B of FIG. 4.

FIG. 6 is a right perspective view of a second pole section shown inFIG. 1.

FIG. 7 is an exploded view of the pole section shown in FIG. 6.

FIG. 8 is a right plan view of the pole section shown in FIG. 6.

FIG. 9 is a vertical cross-sectional view of the pole section shown inFIG. 8, taken generally on line B-B of FIG. 8.

FIG. 10 is a side view of a first laminate geometry.

FIG. 11 is a side view of a second laminate geometry.

FIG. 12 is a side view of a third laminate geometry.

FIG. 13 is a side view of a forth laminate geometry.

FIG. 14 is a side view of a fifth laminate geometry.

FIG. 15 is a right side view of the center ring shown in FIG. 2.

FIG. 16 is a right side view of the center ring shown in FIG. 15.

FIG. 17 is an enlarged detailed view of the center ring shown in FIG.12, taken within the indicated circle of FIG. 12.

FIG. 18 is an exploded perspective view of the fixtures used to assemblethe laminated pole section shown in FIG. 2.

FIG. 19 is an exploded perspective view of the fixture used to assemblea center ring and laminated pole section shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

At the outset, it should be clearly understood that like referencenumerals are intended to identify the same structural elements, portionsor surfaces consistently throughout the several drawing figures, as suchelements, portions or surfaces may be further described or explained bythe entire written specification, of which this detailed description isan integral part. Unless otherwise indicated, the drawings are intendedto be read (e.g., cross-hatching, arrangement of parts, proportion,degree, etc.) together with the specification, and are to be considereda portion of the entire written description of this invention. As usedin the following description, the terms “horizontal”, “vertical”,“left”, “right”, “up” and “down”, as well as adjectival and adverbialderivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”,etc.), simply refer to the orientation of the illustrated structure asthe particular drawing figure faces the reader. Similarly, the terms“inwardly” and “outwardly” generally refer to the orientation of asurface relative to its axis of elongation, or axis of rotation, asappropriate.

This invention provides an improved linear motor, an embodiment of whichis generally indicated at 15. As shown in FIG. 1, linear motor 15generally includes specifically configured stator 16 and mover 19. Mover19 is a cylindrical member elongated about axis x-x and formed of aplurality of annular permanent magnets, severally indicated at 65,spaced axially along its outer circumference. Mover 19 is coincidentwith stator 16 and moves linearly along axis x-x relative to stator 16.Movement along axis x-x is referred to herein as movement in the axialdirection.

As shown in FIGS. 1 and 2, stator 16 is a generally cylindrical memberelongated about axis x-x and having inner opening 18 through which mover19 moves. As shown in FIG. 1, stator 16 is primarily formed from fourpole sections 20-24 that are stacked in the axial direction to formrecesses 25-28 therebetween. Individual stator pole sections 20-24 areglued or bolted together, with coils therebetween, to form stator core16. Stator 16 also includes end pieces, also formed of laminates, whichare fixed by glue, bolts or other means to either end of the stackedpole sections 20-24 to form stator core 16. Recess 25-28 houseconventional coils, which are energized as desired to magneticallyinteract with mover 19 to cause axial movement of mover 19 relative tostator 16. The interior of stator 16 is a cylindrical hollow 18 ofconstant diameter along the length thereof.

As shown in FIGS. 1-14, each individual pole section 20-24 is in turnformed from multiple laminates 17 that are stacked and glued togetheraxially. Thus, the laminates are orientated in a plane that is generallyperpendicular to axis x-x of mover 19. As shown in FIGS. 1-17, each ofpole sections 20-24 also includes inner, specially configuredcylindrical center ring 70 a-70 e, respectively, the inner cylindricalsurfaces of which define opening 18 through which mover 19 reciprocates.

In this embodiment, laminates 17 are formed of a magnetic steellamination material, such as M-15 type, that is either laser-cut orpunched into the desired cross-sectional geometry. The thickness of eachlaminated layer 17 is generally the same. However, the cross-sectionalgeometry of each laminate 17 varies depending on its axial spacedlocation in the subject pole section. The cross-sectional geometry oflaminates 17 are configured so as to form, when stacked and heldtogether with a lamination adhesive, the shape of the respective statorpole section 20-24.

Pole section 21 is shown in more detail in FIGS. 2-5. As shown in FIG.3, pole section 21 is formed by stacking multiple laminates 17 a, havingcross-sectional geometry 29 shown in FIG. 12, together with multiplelaminates 17 b, having cross-sectional geometry 30 shown in FIG. 11,together with multiple laminates 17 c, having cross-sectional geometry33 shown in FIG. 14, together with multiple laminates 17 d, havingcross-sectional geometry 29 shown in FIG. 12. In this embodiment, polesection 21 comprises about 25 individual laminates 17 a having geometry29, about 14 individual laminates 17 b having cross-sectional geometry30, about 25 individual laminates 17 c having cross-sectional geometry33, and about 25 individual laminates 17 d again having cross-sectionalgeometry 29, moving left-to-right along axis x-x with reference to FIG.3. When stacked and glued together, the outer portion of pole section 21is formed. Thereafter, center ring 70 b is pressed into the centeropening of laminated section 21, as further described below.

Pole section 22 is shown in more detail in FIGS. 6-9. As shown in FIG.7, pole section 22 is formed by stacking multiple laminates 17 e, havingcross-sectional geometry 29 shown in FIG. 12, together with multiplelaminates 17 f, having cross-sectional geometry 31 shown in FIG. 10,together with multiple laminates 17 g, having cross-sectional geometry32 shown in FIG. 13, together with multiple laminates 17 h, havingcross-sectional geometry 29 shown in FIG. 12. Thus, pole section 22 maybe varied from pole section 21 by using alternatively-configuredcross-sectional geometry laminates. Whereas the center portion of polesection 21 is formed of multiple laminates 17 b and 17 c havingcross-sectional geometries 31 and 32, respectively, the center portionof pole section 22 is formed of laminates 17 f and 17 g havingalternative cross-sectional geometries 31 and 32, respectively. In thisembodiment, pole section 22 comprises about 25 individual laminates 17 ehaving geometry 29, about 14 individual laminates 17 f havingcross-sectional geometry 31, about 25 individual laminates 17 g havingcross-sectional geometry 32, and about 25 individual laminates 17 hhaving cross-sectional geometry 29, moving left-to-right along axis x-xwith reference to FIG. 7. When stacked and laminated together, the outerportion of pole section 22 is formed. Thereafter, center ring 70 c ispressed into the center opening of laminated section 22, as furtherdescribed below.

It is contemplated that pole sections may be formed with multiplelaminates having various alternative combinations of cross-sectionalgeometries. Thus, while a number of cross-sectional geometries for thelaminates are shown and described, it is contemplated that otheralternative geometries may be employed by one skilled in the art. Havinglaminations that are oriented in planes perpendicular to axis x-x hasbeen unexpectedly found to reduce undesired stator heating and to avoideddy currents.

Laminates 17 a, 17 d, 17 e and 17 h each have cross-sectional geometry29. As shown in FIG. 12, geometry 29 comprises thin ring 35 having outerperimeter 36, inner perimeter 37, thickness 60 between outer perimeter36 and inner perimeter 37, front face 35 a and rear face 35 b. Openingor radial gap 38 is provided between inner perimeter 37 and outerperimeter 36.

Cross-sectional geometry 30 of laminates 17 b is shown in FIG. 11. Asshown, geometry 30 comprises thickened ring 39, having outer perimeter40 and inner perimeter 41. Thickness 42 between outer perimeter 40 andinner perimeter 41 is significantly larger than thickness 60 ofcross-sectional geometry 29. Ring 39 includes front face 39 a andopening 44 between face 39 a and its rear face 39 b. In addition, notch43 is provided at the top extending in from outer perimeter 40. Opening44 is provided so that when multiple laminates 17 b of cross-sectionalgeometry 30 are stacked together, a cylindrical space is provided forhousing a temperature sensor.

Cross-sectional geometry 33 of laminates 17 c is shown in FIG. 14.Cross-sectional geometry 33 comprise ring 55 of the same thickness 58 asthickness 42 of cross-sectional geometry 30. Ring 55 is defined by outerperimeter 56, inner perimeter 57, front face 55 a and a rear face.Cross-sectional geometry 33 includes a specially configured contouredopening 59 between outer perimeter 56 and inner perimeter 57. Opening 59is a relief that provides clearance to allow the last turn of thewindings in respective recesses 25-28 to exit.

Cross-sectional geometer 31, shown in FIG. 10, comprises ring 45 havingfront face 45 a, rear face 45 b, outer perimeter 46, inner perimeter 47and thickness 48 between outer perimeter 46 and an inner perimeter 47,which is the same as thickness 42 of cross-sectional geometry 30 andthickness 48 of cross-sectional geometry 33. This lamination geometry isessentially the same as cross-sectional geometry 30, except that it onlyhas notch 49 and does not include opening 44.

Cross-sectional geometry 32 is shown in FIG. 13, and is similar tocross-sectional geometry 33, shown in FIG. 14. It is formed of ring 50having outer perimeter 51, inner perimeter 52, front face 50 a and acorresponding rear face. It has thickness 53 between outer perimeter 51and inner perimeter 52, which is the same as thicknesses 58, 48 and 42of cross-sectional geometries 33, 31 and 30, respectively. However, theinner portion of relief 54 between inner perimeter 52 and outerperimeter 51 of cross-sectional geometry 32 varies slightly from theinner portion of relief 59 of cross-sectional geometry 33, as shown.

FIGS. 15-17 show inner rings 70 a-70 e. These inner rings are allspecially machined unitary tubular members. As shown in FIG. 16, ring 70is a cylindrical ring-shaped annular structure elongated along axis x-xand generally bounded by rightwardly and downwardly-facing annularangled off-vertical surface 71, rightwardly-facing annular verticalsurface 77, outwardly-facing horizontal cylindrical surface 72,leftwardly-facing annular vertical surface 73, outwardly-facingcylindrical horizontal surface 74, leftwardly and upwardly-facing angledoff-vertical annular surface 75, and inwardly-facing horizontalcylindrical surface 76. Surfaces 73, 72 and 77 define alignmentprotrusion 79. As described below, the small edge 79 machined into ring70 creates a stop such that the pressing of ring 70 into the inneropening of the laminated pole section is repeatable with precision andsuch that axial alignment of the ring is correct. In particular, surface73 of alignment protrusion 79 acts as a stop so that center ring 70extends into the inner perimeter of the subject laminated pole sectionthe desired amount.

As shown in FIG. 17, alignment protrusion 79 includes alignment notch 80extending inwards from surface 72. Alignment notch 80 is used torotationally align ring 70 with the laminated pole section into which itis inserted.

As shown in FIGS. 1, 5, 9 and 16, center ring 70 is machined as a solidsteel ring that is pressed into the center of an assembled laminatedpole section in order to create skew in stator 16 and reduce coggingforces in motor 15. As shown in FIG. 16, surfaces 71 and 75 are parallelannular surfaces and are angled off-vertical by skew angle 88. In thisembodiment, skew angle 88 is about 3.2 degrees. Because of thepositioning of center ring 70 within the subject laminated pole section,center ring 70 forms the inner tooth of the pole piece. It has beenfound that the skew of ring 70 and its placement helps to reduce torqueripple and provides unexpected and improved performance characteristics.As shown in FIG. 1, pole sections 20-24, together with the end sectionsare stackable at axial spaced locations along axis x-x. Also as shown,each of the laminated pole sections 20-24 includes skewed center rings70 a-70 e, respectively, which are pressed into the inner opening of thelaminated portion of the pole section until projections 79 a-70 e,respectively, abut against the leftwardly-facing surface of the subjectstator pole section. Thus, ring 70 b is pressed into the center openingof the laminated portion of pole section 21 until surface 73 ofprojection 79 b abuts against and is stopped by leftwardly-facingsurface 39 b of pole section 21. Similarly, ring 70 c is pressed intothe center opening of the laminated portion of pole section 22 untilannular surface 73 of projection 79 c abuts against and is stopped byleftwardly-facing surface 45 b of pole section 22.

FIG. 18 shows the use of fixtures 100 and 103 to properly alignlaminates 17 a-17 e about axis x-x relative to each other when formingpole section 21. As shown, fixture 100 is a generally cylindrical memberhaving an outer perimeter and an inner perimeter. Two outer positioningrods 86 a and 86 b extend from the left face of fixture 100 parallel toaxis x-x. In addition, three inner positional rods 90 a-90 c extend fromthe left face of fixture 100 parallel to axis x-x. Also, three shorterpositional rods 91 a-91 c extend from the left face of fixture 100parallel to axis x-x. Inner rods 90 a-90 c are positioned on fixture 100such that an imaginary circle drawn about all three rods has a diameterthat is substantially equal to the diameter of inner perimeter 41, 57 ofgeometry 30, 33 of laminates 17 b and 17 c, respectively. Rods 91 a-91 care positioned on fixture 100 such that an imaginary circle drawn aboutall three rods has a diameter that is substantially equal to thediameter of inner perimeter 37 of geometry 29 of laminates 17 a and 17d. Rods 86 a and 86 b are in turn positioned on fixture 100 separatedfrom each other a distance approximately equal to the distance betweenedges 85 a and 85 b of notches 38, 43, 49, 54 and 59. As shown, fixture103 is a generally cylindrical member having an outer perimeter and aninner perimeter. Three shorter positional rods 92 a-92 c extend from theright face of fixture 100 parallel to axis x-x. Inner rods 90 a, 92 b(not shown) and 92 c (not shown) are positioned on fixture 100 to matchthe location of rods 91 a-91 c on fixture 100, such that an imaginarycircle drawn about all three rods has a diameter that is substantiallyequal to the diameter of inner perimeter 37 of geometry 29 of laminates17 a and 17 d. Thus, all of the required laminates may be slipped overthe rods and stacked on fixtures 100 and 103 so that they are allproperly rotationally aligned relative to each other.

In particular, spacer 101 is first aligned and positioned on fixture 100with rods 86 a-86 b and 91 a-91 c extending through the respectivecorresponding openings in spacer 101 and rods 90 a-c extending throughthe center opening of spacer 101. Next, laminates 17 a havingcross-sectional geometry 29 are positioned and slipped over the rods offixture 100 such that rods 86 a and 86 b extend between the opposedsides of gap 38 of cross-sectional geometry 29 of laminates 17 a, androds 91 a-91 c fit within and support inner perimeter 37 ofcross-sectional geometry 29 of laminates 17 a. Next, laminates 17 bhaving cross-section geometry 30 are positioned and slipped over therods of fixture 100 such that arms 86 a and 86 b extend between theouter opposed sides of notch 43 of cross-sectional geometry 30 oflaminates 17 b, and rods 90 a-90 c fit within and support innerperimeter 41 of cross-sectional geometry 30 of laminates 70 b. Next,laminates 17 c having cross-sectional geometry 33 are positioned andslipped over the rods of fixture 100 such that arms 86 a and 86 b extendbetween the outer opposed sides of opening 59 of cross-sectionalgeometry 33 of laminates 17 c, and arms 90 a-90 c fit within and supportinner perimeter 57 of cross-sectional geometry 33 of laminates 17 c.Next, laminates 17 d having cross-sectional geometry 29 are positionedand slipped over the rods of fixture 100 such that rods 86 a and 86 bextend between the opposed sides of gap 38 of cross-sectional geometry29 of laminates 17 d. Next, spacer 102 is aligned and positioned onfixture 100 with rods 86 a-86 b extending through the respectivecorresponding openings in spacer 102 and rods 90 a-90 c extendingthrough the center opening of spacer 102. End fixture 103 is thenaligned and positioned in fixture 100 such that rods 86 a and 86 b offixture 100 extend through the corresponding openings in end fixture 103and such that rightward-extending rods 92 a-92 c of fixture 103extending through the respective corresponding openings in spacer 102and then in turn fit within and inner perimeter 37 of cross-sectionalgeometry 29 of laminates 17 d. With laminate adhesive between laminatelayers 17 a-17 d, fixture 100 and fixture 103 are then pressed againsteach other while the adhesive of the assembly cures. In this manner, thestator pole section laminations are assembled in a fixture which alignseach of the lamination pieces in the proper orientation while theadhesive cures so that a fully assembled laminated pole section isprovided.

Pole section 22 is formed in a similar manner. In particular, spacer 101is first aligned and positioned on fixture 100 with rods 86 a-86 b and91 a-91 c extending through the respective corresponding openings inspacer 101 and rods 90 a-90 c extending through the center opening ofspacer 101. Next, laminates 17 e having cross-sectional geometry 29 arepositioned and slipped over the rods of fixture 100 such that rods 86 aand 86 b extend between the opposed sides of gap 38 of cross-sectionalgeometry 29 of laminates 17 e, and rods 91 a-91 c fit within and supportinner perimeter 37 of cross-sectional geometry 29 of laminates 17 e.Next, laminates 17 f having cross-section geometry 31 are positioned andslipped over the rods of fixture 100 such that arms 86 a and 86 b extendbetween the outer opposed sides of notch 49 of cross-sectional geometry31 of laminates 17 f, and rods 90 a-90 c fit within and support innerperimeter 47 of cross-sectional geometry 31 of laminates 70 f. Next,laminates 17 g having cross-sectional geometry 32 are positioned andslipped over the rods of fixture 100 such that arms 86 a and 86 b extendbetween the outer opposed sides of opening 54 of cross-sectionalgeometry 32 of laminates 17 g, and arms 90 a-90 c fit within and supportinner perimeter 52 of cross-sectional geometry 32 of laminates 17 g.Next, laminates 17 h having cross-sectional geometry 29 are positionedand slipped over the rods of fixture 100 such that rods 86 a and 86 bextend between the opposed sides of gap 38 of cross-sectional geometry29 of laminates 17 h. Next, spacer 102 is aligned and positioned onfixture 100 with rods 86 a-86 b extending through the respectivecorresponding openings in spacer 102 and rods 90 a-c extending throughthe center opening of spacer 102. End fixture 103 is then aligned andpositioned in fixture 100 such that rods 86 a and 86 b of fixture 100extend through the corresponding openings in end fixture 103 and suchthat rightward-extending rods 92 a-92 c of fixture 103 extending throughthe respective corresponding openings in spacer 102 and then in turn fitwithin and inner perimeter 37 of cross-sectional geometry 29 oflaminates 17 h. With laminate adhesive between laminate layers 17 e-17h, fixture 100 and fixture 103 are then pressed against each other whilethe adhesive of the assembly cures.

FIG. 19 is a representative view showing the use of fixture 81 and press84 to combine ring 70 with the laminated portion of each pole sectionformed as described above. In particular, fixture 81 is provided toproperly align ring 70 in the center opening of the laminated portion ofpole section 20-24. As shown, fixture 81 is a specially configuredcylindrical member having an outer perimeter and an inner perimeterdefining a center opening. Alignment key 82 extends from the outerperimeter of fixture 81. The outer perimeter of fixture 81 has adiameter that is substantially equal to the diameter of inner perimeter37 of geometry 29 of laminates 17 a. Alignment key 82 extends beyondthat perimeter and has a width that is to the width of gap 38 ofcross-sectional geometry 29 of laminates 17 a. Thus, if aligned properlyabout axis x-x, fixture 81 should fit within the recess of pole section21 formed by laminates 17 a such that its outer perimeter is encompassedwithin inner perimeter 37 of geometry 29 of laminates 17 a and alignmentkey projection 82 fits through opening 38 of geometry 29 of laminates 17a.

The inner perimeter of fixture 81 has a diameter that is substantiallyequal to the diameter of surface 72 of projection 79 b of ring 70 b.Thus, ring 70 b slides within the inner perimeter of fixture 81 if andwhen ring 70 b is properly rotationally aligned such that innerprojection 83 slides axially into notch 80 in projection 79 b of ring 70b. Thus, to properly align ring 70 b in the laminated portion of polesection 21, ring 70 b is rotationally aligned with fixture 81 such thatprojection 83 axially slides into notch 80 and the outer perimeter ofalignment projection 79 b is within the inner perimeter of fixture 81.

So first ring 70 b is rotationally aligned with fixture 81 such thatprojection 83 axially slides into notch 80 and the outer perimeter ofalignment projection 79 b is within the inner perimeter of fixture 81.Once ring 70 b is rotationally aligned within the inner perimeter offixture 81, fixture 81 is aligned with the laminated portion of polesection 21 such that outer alignment key 82 slides within the gap formedby opening 38 of geometry 29 in laminates 17 a. This assures thatfixture 81 is rotationally aligned properly with the laminated portionof pole section 21. Press 89 is then used to force ring 70 into thecenter opening of the laminated portion of pole section 21. Ring 70 ispressed into the center opening of the laminated portion of pole section21 until annular surface 73 of alignment projection 79 b abuts and isstopped by leftward-facing surface 39 b of pole section 21. In thismanner, ring 70 is rotationally aligned about axis x-x relative to polesection 21 and is axially aligned along axis x-x relative to laminatepole section 21. This method of both rotationally and axially aligningring 70 b into the center opening of laminated pole section 21 providesfor repeatability, precision and accurate ring positioning so that aproper skew is provided. The same process is employed with respect tothe other pole sections.

Once each of the pole sections, with its respective center ring, areformed, they are in turn stacked axially in the desired configuration toform stator core 16 with windings as required in recesses 25, 26, 27 and28. In addition, temperature gages and the like may be positioned in thespecially configured openings, for example opening 44, when the polesections are stacked together. In this manner, any combination orconfiguration of laminates, laminated pole sections or pole core may beformed as desired.

The present invention contemplates that many changes and modificationsmay be made. For example, the assembled stator core may be fitted insidea magnetic tube which adds an additional magnetic flux path, therebyimproving the force generated by the motor. Such pipe may be ordinary ormagnetic stainless steel for improved corrosion resistance. The magneticlamination material of laminates 17 may be of various grades or havevarious magnetic properties, depending on the performance versus costdesired. The diameter size of the stator components are scalable,depending on the performance desired from the final motor. The length ofthe assembled stator, the axial thickness of the pole sections, and thenumber of pole sections are scalable, again depending on the performancedesired and the practical manufacturing limits of the components. Thecross-sectional geometries of the individual laminates may be varied asdesired. The number and geometries of the pole sections may be varied asdesired. Therefore, while the presently preferred form of the linearmotor has been shown and described, those persons skilled in this artwill readily appreciate the various additional changes and modificationmay be made without departing from the spirit of the invention, asdefined and differentiated by the following claims.

The invention claimed is:
 1. A linear motor comprising: a stator havingan opening; a mover disposed in said opening and configured and arrangedto reciprocate linearly in an axial direction relative to said stator;said stator comprising a first pole section and a second pole sectionstacked in said axial direction and forming a recess between them forreceiving annular windings; said first pole section comprising a firstlaminate having a first cross-sectional geometry; said first polesection comprising a second laminate having a second cross-sectionalgeometry different from said first cross-sectional geometry; said firstlaminate and said second laminate stacked in said axial direction; saidfirst pole section comprising a third laminate having a thirdcross-sectional geometry different from said first cross-sectionalgeometry and said second cross-sectional geometry; and said thirdlaminate stacked in said axial direction with said first laminate andsaid second laminate.
 2. The linear motor set forth in claim 1, whereinsaid first pole section further comprises a fourth laminate having saidfirst cross-sectional geometry and stacked in said axial direction withsaid first, second and third laminates.
 3. The linear motor set forth inclaim 1, wherein said first pole section comprises multiple laminateshaving said first cross-sectional geometry and multiple laminates havingsaid second cross-sectional geometry and stacked in said axialdirection.
 4. The linear motor set forth in claim 1, wherein said firstcross-sectional geometry of said first laminate comprises an annularring having an outer perimeter and an inner perimeter.
 5. A linear motorcomprising: a stator having an opening; a mover disposed in said openingand configured and arranged to reciprocate linearly in an axialdirection relative to said stator; said stator comprising a first polesection and a second pole section stacked in said axial direction andforming a recess between them for receiving annular windings; said firstpole section comprising a first laminate having a first cross-sectionalgeometry and a second laminate having a second cross-sectional geometrydifferent from said first cross-sectional geometry; said first laminateand said second laminate stacked in said axial direction; said firstcross-sectional geometry of said first laminate comprising an annularring having an outer perimeter and an inner perimeter; and said annularring comprising an opening between said outer perimeter and said innerperimeter.
 6. A linear motor comprising: a stator having an opening; amover disposed in said opening and configured and arranged toreciprocate linearly in an axial direction relative to said stator; saidstator comprising a first pole section and a second pole section stackedin said axial direction and forming a recess between them for receivingannular windings; said first pole section comprising a first laminatehaving a first cross-sectional geometry and a second laminate having asecond cross-sectional geometry different from said firstcross-sectional geometry; said first laminate and said second laminatestacked in said axial direction; said first cross-sectional geometry ofsaid first laminate comprising an annular ring having an outer perimeterand an inner perimeter; and said second cross-sectional geometry of saidsecond laminate comprising an annular ring having an outer perimeter andan inner perimeter and a radial thickness between them greater than aradial thickness of said annular ring of said first cross-sectiongeometry.
 7. The linear motor set forth in claim 6, wherein said annularring of said second cross-sectional geometry of said second laminatecomprises a shaped opening between said outer perimeter and said innerperimeter.
 8. The linear motor set forth in claim 6, wherein saidannular ring of said second cross-sectional geometry of said secondlaminate comprises a first face and a second face and an opening betweensaid first face and said second face.
 9. The linear motor set forth inclaim 8, wherein said annular ring of said second cross-sectionalgeometry of said second laminate comprises a notch extending towardssaid inner perimeter from said outer perimeter.
 10. A linear motorcomprising: a stator having an opening; a mover disposed in said openingand configured and arranged to reciprocate linearly in an axialdirection relative to said stator; said stator comprising a first polesection and a second pole section stacked in said axial direction andforming a recess between them for receiving annular windings; said firstpole section comprising a first laminate having a first cross-sectionalgeometry and a second laminate having a second cross-sectional geometrydifferent from said first cross-sectional geometry; said first laminateand said second laminate stacked in said axial direction; and a centerring element within said first pole section and defining said opening ofsaid stator.
 11. The linear motor set forth in claim 10, wherein saidcenter ring element comprises: an inner perimeter configured to defineat least in part said stator opening and an outer perimeter configuredto fit at least in part within said inner perimeter of said first polesection; a first facing surface and a second facing surface; and saidfirst facing surface skewed relative to an imaginary plane orientatedgenerally perpendicular to said axial direction of said mover such thatsaid first facing surface is not parallel to said plane orientatedgenerally perpendicular to said axial direction of said mover.
 12. Thelinear motor set forth in claim 11, wherein said second facing surfaceis skewed relative to said plane perpendicular to said axial directionand is parallel to said first facing surface.
 13. The linear motor setforth in claim 11, wherein said first pole section comprises a firstfacing surface orientated in a plane generally perpendicular to saidaxial direction of said mover and said outer perimeter of said centerring element comprises an axial alignment projection configured andarranged to extend radially outward at least in part beyond said innerperimeter of said first pole section and to abut against said firstfacing surface of said first pole section.
 14. The linear motor setforth in claim 13, wherein said axial alignment projection comprises anannular contact surface orientated in a plane generally perpendicular tosaid axial direction of said mover.
 15. The linear motor set forth inclaim 11, wherein said center ring element comprises a solid unitarysteel tube.
 16. A linear motor comprising: a stator having an opening; amover disposed in said opening and configured and arranged toreciprocate linearly in an axial direction relative to said stator; saidstator comprising a first pole section and a second pole section stackedin said axial direction and forming a recess between them for receivingannular windings; said first pole section comprising a first laminatehaving a first cross-sectional geometry and a second laminate having asecond cross-sectional geometry different from said firstcross-sectional geometry; and said first laminate and said secondlaminate of said first pole section stacked in said axial direction;said second pole section comprising a first laminate having a firstcross-sectional geometry and a second laminate having a secondcross-sectional geometry different from said first cross-sectionalgeometry; and said first laminate and said second laminate of saidsecond pole section stacked in said axial direction.
 17. The linearmotor set forth in claim 16, wherein said second pole section furthercomprises a third laminate having a third cross-sectional geometrydifferent from said first cross-sectional geometry and said secondcross-sectional geometry and stacked in said axial direction with saidfirst laminate and said second laminate.
 18. The linear motor set forthin claim 17, wherein said second pole section further comprises a fourthlaminate having said first cross-sectional geometry and stacked in saidaxial direction with said first, second and third laminates.
 19. Thelinear motor set forth in claim 16, wherein said second pole sectioncomprises multiple laminates having said first cross-sectional geometryand multiple laminates having said second cross-sectional geometry andstacked in said axial direction.
 20. The linear motor set forth in claim19, and further comprising a center ring element within said second polesection and defining said opening of said stator.
 21. The linear motorset forth in claim 20, wherein said center ring element comprises: aninner perimeter configured to define at least in part said statoropening and an outer perimeter configured to fit at least in part withinsaid inner perimeter of said second pole section; a first facing surfaceand a second facing surface; and said first facing surface skewedrelative to an imaginary plane orientated generally perpendicular tosaid axial direction of said mover such that said first facing surfaceis not parallel to said plane perpendicular to said axial direction ofsaid mover.
 22. The linear motor set forth in claim 21, wherein saidsecond facing surface is skewed relative to said plane perpendicular tosaid axial direction and is parallel to said first facing surface. 23.The linear motor set forth in claim 21, wherein said second pole sectioncomprises a first facing surface orientated in a plane generallyperpendicular to said axial direction of said mover and said outerperimeter of said center ring element comprises an axial alignmentprojection configured and arranged to extend radially outward at leastin part beyond said inner perimeter of said second pole section and toabut against said first facing surface of said second pole section. 24.The linear motor set forth in claim 23, wherein said axial alignmentprojection comprises an annular contact surface orientated in a planegenerally perpendicular to said axial direction of said mover.
 25. Alinear motor comprising: a stator having an opening; a mover disposed insaid opening and configured and arranged to reciprocate linearly in anaxial direction relative to said stator; said stator comprising a firstpole section and a second pole section stacked in said axial directionand forming a recess between them for receiving annular windings; saidfirst pole section comprising a first laminate having a firstcross-sectional geometry and a second laminate having a secondcross-sectional geometry different from said first cross-sectionalgeometry; said first laminate and said second laminate stacked in saidaxial direction; said first pole section comprising a first center ringelement and said second pole section comprising a second center ringelement; each of said first center ring element and said second centerring element comprising an inner perimeter configured to define at leastin part said stator opening and an outer perimeter configured to fit atleast in part within said inner perimeter of said respective polesection, a first facing surface and a second facing surface, and saidfirst and second facing surfaces skewed relative to an imaginary planeorientated generally perpendicular to said axial direction of said moversuch that said first and second facing surfaces are not parallel to saidplane orientated generally perpendicular to said axial direction of saidmover; wherein said skew of said second facing surface of said firstcenter ring element of said first pole section is substantially equal tosaid skew of said first facing surface of said second center ringelement of said second pole section; and wherein said first center ringelement and said second center ring element are stacked in said axialdirection to form at least in part said opening of said stator.
 26. Thelinear motor set forth in claim 25, wherein said skew is configured andarranged to reduce cogging forces in said motor.
 27. A linear motorcomprising: a stator having an opening; a mover disposed in said openingand configured and arranged to reciprocate linearly in an axialdirection relative to said stator; said stator comprising a first polesection and a second pole section stacked is said axial direction andforming a recess between them for receiving annular windings; said firstpole section having an outer perimeter and an inner perimeter; a centerring element having an inner perimeter configured to define at least inpart said stator opening and an outer perimeter configured to fit atleast in part within said inner perimeter of said first pole section;said center ring element further comprising a first facing surface and asecond facing surface; and said first facing surface skewed relative toan imaginary plane orientated generally perpendicular to said axialdirection of said mover such that said first facing surface is notparallel to said plane orientated generally perpendicular to said axialdirection of said mover.
 28. The linear motor set forth in claim 27,wherein said second facing surface is skewed relative to said planeperpendicular to said axial direction and is parallel to said firstfacing surface.
 29. The linear motor set forth in claim 27, wherein saidfirst pole section comprises a first facing surface orientated in aplane generally perpendicular to said axial direction of said mover andsaid outer perimeter of said center ring element comprises an axialalignment projection configured and arranged to extend at least in partbeyond said inner perimeter of said first pole section and to abutagainst said first facing surface of said first pole section.
 30. Thelinear motor set forth in claim 29, wherein said axial alignmentprojection comprises an annular contact surface orientated in a planegenerally perpendicular to said axial direction of said mover.
 31. Thelinear motor set forth in claim 27, wherein said center ring elementcomprises a solid unitary steel tube.
 32. The linear motor set forth inclaim 27, wherein said first pole section and said second pole sectionare provided with a rotational alignment contour.
 33. The linear motorset forth in claim 32, wherein said rotational alignment contourcomprises an axial notch.
 34. The linear motor set forth in claim 27,wherein: said first stator pole section comprises a pole sectionrotational alignment contour corresponding to a first rotationalalignment key of a ring rotational alignment fixture; and said centerring element comprises a ring rotational alignment contour correspondingto a second rotational alignment key of said ring rotational alignmentfixture.
 35. The linear motor set forth in claim 34, wherein said polesection rotational alignment contour comprises an axial notch, saidfirst rotational alignment key comprises a tab corresponding to saidnotch, said ring rotational alignment contour comprises an axial notch,and said second rotational alignment key comprises a protrusioncorresponding to said notch of said ring rotational alignment contour.